Plasma Dynamical Processes and Turbulence Studies using Advanced Microwave Diagnostics

Frequency diplexers for comb reflectometers

Background: By varying the microwave probing frequency different plasma radii can be probed. Instead of sweeping or stepping the frequency in time an alternative is the comb reflectometer. Here, efficient combining/separating of several fixed probe frequencies (typically > 5) onto common antennas is used. This allows simultaneous measurements at several locations.

Approach: Standard technology uses e.g. 3dB directional couplers, with a concomitant loss of combined source power. However, by using multi-mode interference in oversized waveguides and/or by quasi-optical resonator techniques, low-loss diplexers can be designed, which can be used as directional couplers and allow the staggering of several devices.

Frequency diplexers based on spatial and angular Talbot effects have already been developed at IGVP. An optimization algorithm was used to find the waveguide dimensions for optimal performance at two frequencies. Based on these results and the fact that higher
insertion losses (1dB) remain uncritical for reflectometry applications it will be possible to extend the optimization codes for diplexing of multiple frequencies and to explore the possible frequency spacing and number of channels etc.

Project lead by IGVP:
      Dr. Burkhard Plaum
      PhD student (t.b.a.)
      Dr. Walter Kasparek

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Dr. Burkhard Plaum